Near-eye display (NED) devices typically include separate waveguides for the left eye and the right eye of a user wearing the display. The waveguides each include a projector that produces a small pupil of optical light to a circular in-coupling region of the waveguide, which can be referred to as an optical input port, and a diffractive optical element that expands the pupil horizontally and diffracts the light downward towards an output port. The output port couples to the display module to display an image, such as a left eye image from a left eye waveguide in a left eye region of the display module, and a right eye image from a right eye waveguide in a right eye region of the display module.
The display module is positioned at an eye-relief distance from the user's eye to account for the user possibly wearing spectacles, varying head shapes and eye locations, etc. Problems can arise when the field-of-view output by the waveguides extends beyond a threshold (e.g., 60 degrees) where one eye can gaze both left and right waveguides at the same time. This can cause confusion as each waveguide includes only portions of an image intended for the given eye. In addition, a mechanical interference between the left and right waveguides can set a hard limit to the waveguide lateral size, which can exacerbate this issue as the eye-relief distance increases. Other smart glass display technologies, such as free form prisms and curved reflectors, may exhibit similar issues.